1. Field of the Invention
The present invention relates to systems for controlling the power applied to a load and the temperature within a medium being increased or decreased by the load and more particularly is disclosed as it would be adapted to control appliances and the like such as a microwave oven.
Generally speaking, the control system of the present invention includes a variable power and temperature control circuit which utilizes a unique oscillator circuit to provide various levels of power to the microwave oven magnetron in response to both user selectivity and the temperature being sensed.
2. Description of the Prior Art
In those prior art control systems which allow the user of a microwave oven to select a desired power level to be applied to the oven magnetron, the variable power source usually includes an oscillator circuit having a variable period which is a function of the means for selecting the desired power level. Most of these prior art variable power sources apply power to the magnetron at the level desired and completely deactivate the magnetron either when a time period has expired or when a desired temperature is reached. However, in a microwave oven it is many times desirable after the food has been cooked that the oven keep the food warm until the user can either remove the food or otherwise reprogram the oven.
As a result of the disadvantages of prior art variable power and/or temperature control systems described above, such control systems are expensive and many times not as reliable as they could be. By improving upon the design of these older systems the cost can be reduced while at the same time increasing reliability and performance.